The present invention pertains generally to ophthalmic surgery and measurements, particularly for identification and/or correction of optical vision deficiencies. In exemplary embodiments, the present invention provides systems and methods for planning and performing cataract surgery, including selection and/or placement of an intraocular lens (IOL) within an eye.
Laser corneal shaping or corrective refractive surgeries are commonly used to treat myopia, hyperopia, astigmatism, and the like. Laser refractive procedures include LASIK and (Laser Assisted In-Situ Keratomileusis), Photorefractive Keratectomy (PRK), Epithelial Keratomileusis (LASEK or Epi-LASEK), and Laser Thermal Keratoplasty. Alternative refraction altering procedures which do not rely on lasers, and/or which do not alter the corneal shape, have also been described.
During LASIK, a surgeon makes a cut part way through a front surface of a cornea, optionally using an oscillating steel blade or microkeratome. The microkeratome automatically advances the blade through the cornea so as to create a thin flap of clear tissue on the front central portion of the eye. The flap can be folded over to expose stromal tissue for selective ablation with an excimer laser. More recently, femtosecond laser systems have been developed to form laser incision in the corneal tissue so as to cut the corneal flap without using a mechanical blade. Regardless of how the flap is prepare, the excimer laser corrects a visual defect by directing a beam of pulsed laser energy onto the exposed corneal stroma. Each laser pulse from the excimer laser removes a very small and precise amount of corneal tissue so that the total removal of stromal tissue from within the cornea alters and corrects the refractive properties of the overall eye. After removal (and more specifically, after laser ablation) of the desired stromal tissue, the flap can be folded back over the ablated surface. The flap of protective epithelial tissue quickly and naturally reattaches over the resculpted stromal tissue, and the eye retains much of the effective alteration in shape after the cornea heals.
A number of alternative laser refractive procedures have been used and/or are being developed. In one variation, rather than incising the corneal tissue for temporary displacement of an epithelial flap, the epithelium may be ablated (typically using the excimer laser) or abraded in a PRK procedure. As an alternative to resculpting the stroma using an excimer laser, it has also been proposed to form incisions within the cornea or other refractive tissues of the eye with the femtosecond laser. These femtosecond laser procedures include corneal lenticule extractions, as well as making relaxing incisions in the cornea to correct the eye's refractive properties. Still further alternatives have been described, and new procedures are being developed to further enhance the capabilities of refractive corrections using lasers and other refractive tissue altering tools.
Known corneal correction treatment methods have generally been quite successful in correcting standard vision errors, such as myopia, hyperopia, and astigmatism. However, as with all successes, still further improvements have become desirable. Toward that end, wavefront measurement systems are now available to measure the refractive characteristics of a particular patient's eye. These wavefront measurement systems allow accurate measurement of the overall aberrations of the optical system of the eye, providing quite detailed information on the high-order optical aberrations that may limit a patient's visual acuity even after the standard refractive errors have been corrected (for example, by eye glasses, contact lenses, and the like). Still additional measurement tools may provide information which is useful for such customized ablation procedures. For example, corneal topographers are commercially available that can provide quite accurate information regarding the shape of the anterior surface of the cornea, and this surface may have a significant role in the overall optical properties of the eye. Optical coherence tomographers (OCT) may provide information regarding both the anterior and interior surfaces of the eye. By combining these accurate measurement tools with the flexibility of modern scanning excimer lasers, custom refractive corrections should correct not only the standard refractive errors of the eye, but also address the specific high-order aberrations of a particular patient.
Although customized laser and other refractive treatments have provided significant benefits for many patients, the overall improvement in refractive performance of the eyes of patients treated using these new techniques has not yet achieved their full theoretical potential. A number of theories or factors have been proposed to help explain why some customized ablation procedures have not altogether eliminated high-order aberrations of the eye. Even when laser refractive corrections were limited to the standard refractive errors of myopia, hyperopia, and astigmatism, the empirical response of prior treatments led to doctors applying discrete adjustment factors or “nomograms” so as to adjust a calculated prescription before imposing the treatment on an eye of a patient. Significant efforts have gone toward increasing the benefit of both standard and customized refractive corrections by identifying analogous nomogram adjustments for high-order aberration corrections. Unfortunately, work in connection with the present invention indicates the challenges of identifying suitable nomogram adjustments for a customized refractive correction for a particular patient in a particular treatment setting may continue to limit the benefits of customized corneal ablations to significantly less than the ideal potential outcomes. In fact, a significant number of high-order refractive treatments may result in other high-order aberrations of the eye actually increasing (even where the visual acuity of the eye overall benefits from the treatment).
Cataract extraction is another frequently performed surgical procedure. A cataract is formed by opacification of the crystalline lens of the eye. The cataract scatters light passing through the lens and may perceptibly degrade vision. A cataract can vary in degree from slight to complete opacity. Early in the development of an age-related cataract, the power of the lens may increase, causing near-sightedness (myopia). Gradual yellowing and opacification of the lens may reduce the perception of blue colors as those shorter wavelengths are more strongly absorbed and scattered within the cataractous crystalline lens. Cataract formation may often progress slowly resulting in progressive vision loss.
A cataract treatment may involve replacing the opaque crystalline lens with an artificial intraocular lens (IOL). Cataract surgery can be performed using a technique termed phacoemulsification in which an ultrasonic tip with associated irrigation and aspiration ports is used to emulsify or sculpt the relatively hard nucleus of the lens to facilitate removal through an opening made in the anterior lens capsule. The nucleus of the lens is contained within an outer membrane of the lens that is referred to as the lens capsule. Access to the lens nucleus can be provided by performing an anterior capsulotomy in which a small round hole can be formed in the anterior side of the lens capsule using a femtosecond laser beam from a laser cataract surgical system. Access to the lens nucleus can also be provided by performing a manual continuous curvilinear capsulorhexis (CCC) procedure using microkeratomes. A femtosecond laser can also be used to soften and break up the cataractous lens so that less energy from phacoemulsification is required for lens extraction. An alternative to phacoemulsification is manual small incision cataract surgery (MSICS), a procedure where the entire lens is expressed out of the eye through a self-sealing scleral tunnel wound.
Regardless of how the lens nucleus is removed, after this is accomplished, a synthetic intraocular lens (IOL) is then inserted into the remaining lens capsule of the eye to replace the cataractous lens.
Planning a cataract treatment can be a challenging problem. Before performing cataract surgery, the surgeon will need to select appropriate parameters for the IOL (e.g., the refractive power of the IOL) to be implanted (much like an eyeglass prescription) to provide the patient with the desired refractive outcome.
There is significant variation from patient-to-patient (or eye-to-eye) in many important eye biometric parameters, each of which may affect surgical planning, treatment and outcome. Moreover, many patients may have biometric configurations, including for example, corneal lower order and higher order aberrations, extreme axial lengths, and/or previous corneal refractive treatments such as LASIK, which may also affect surgical planning, treatment, and outcome. For example, with respect to eye aberrations, some patients have near-sightedness (myopia), far-sightedness (hyperopia), or astigmatism. Near-sightedness occurs when light focuses in front of the retina, while far-sightedness occurs when light refracts to a focus behind the retina. Astigmatism occurs when the corneal curvature is unequal in two or more directions. Various surgical methods have been developed and used to treat these types of aberrations.
Ideally, for best results and outcome, a cataract surgeon would have access to not only ocular biometry information, but also to information on the eye's anterior corneal surface, posterior corneal surface, anterior lens surface, posterior lens surface, lens tilt, lens thickness, and lens position in order to plan cataract treatment pre-operatively, and/or to assess the post-operative refractive state of a patient's eye with the implanted IOL.
Traditionally, doctors use preoperative measurements including corneal curvature, axial length, and white to white measurements to estimate the required power of the IOL, and apply the measured data to formulas such as Hagis, Hoffer Q, Holladay 1, Holladay 2, and SRK/T to name a few, to select the appropriate power of the IOL to be implanted.
A variety of optical measurement systems have been developed, each of which provides a limited subset of the desired measurements. Hence, a cataract patient may currently be required to undergo a number of measurements performed on different devices—if the measurements are taken at all. There is a significant disadvantage in using multiple measurement devices in cataract planning because the patient's eye may be in a different position, it may have changed between measurements, or the measurements may be made under different conditions, etc. Further, there may be no way to combine or fuse the data sets from different devices to obtain a single, three-dimensional model of the patient's eye.
Studies have shown that refractive results using traditional eye measurement techniques and traditional IOL power calculation formulas leave patients within 0.5D of target (correlates to 20/25 when targeted for distance) or better in 55% of cases and within 1D (correlates to 20/40 when targeted for distance) or better in 85% of cases. Still, this means that in a significant percentage of cases, significantly less-than-optimal results are achieved and there is substantial room for improvement in the techniques employed for cataract surgery planning.
In light of the above, it would be beneficial to provide improved devices, systems, and methods for measuring, diagnosing and/or treating defects of an eye of a cataract patient. Preferably, these improved techniques would still allow physicians to input nomogram adjustments for a particular patient. It would be particularly beneficial if these improvements were able to increase the overall accuracy with which high-order aberrations of an eye could be treated, ideally without significantly increasing the cost or complexity of measurement and/or treatment systems.
In light of the above, it would also be beneficial to provide improved devices, systems, and methods for making eye measurements for diagnosing and/or treating cataracts. It would be particularly beneficial if these improvements were able to increase the overall accuracy with which intraocular lenses for cataract surgery could be specified, selected, and located within an eye, ideally without significantly increasing the cost or complexity of measurement, diagnosis, and/or treatment systems.